MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
DECEMBER, 2000
(For general comments about the nature of these summaries, as well as
information on how to download the tabular cyclone track files, see
the Author's Note at the end of this summary.)
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DECEMBER HIGHLIGHTS
--> Intense tropical cyclone strikes Northwestern Australia
--> Intense typhoon rapidly intensifies, then rapidly weakens
--> Cyclone of hurricane intensity strikes Sri Lanka
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***** Feature of the Month for December *****
ATLANTIC SUBTROPICAL SYSTEMS OF 2000
(Part 3)
------------------------------------
This is Part 3 of a three-part feature detailing cyclonic systems
of 2000 in the Atlantic which were either subtropical storms or
depressions or else exhibited some of the features of subtropical
cyclones. The information presented below is taken from material
supplied by David Roth of HPC. Please refer to Part 1 in the October
summary for more background information and some explanations and
caveats.
I am repeating here the table of subtropical/hybrid systems which
David provided. (Numbers in parentheses following the storm
designation refer to explanatory notes below.)
I. Subtropical Depression May 19-25
II. Alberto (1) August 14-16
III. Subtropical Storm (2) August 28-30
IV. Subtropical Depression September 10-11
V. Florence (3) September 10-12
VI. Gordon (1) September 17-18
VII. Helene (1) September 24-25
VIII. Subtropical Storm (2) September 30-October 3
IX. Leslie (3) October 4-8
X. Michael (3) October 14-17
XI. Subtropical Storm (4) October 25-28
(1) The official NHC "best tracks" do not treat any portion of Alberto,
Gordon, or Helene as subtropical. In general, once a tropical
cyclone has been named, NHC treats it as a tropical system through-
out the remainder of its life--both operationally and in post-
analysis--even if at some point it exhibited some subtropical
features.
(2) According to Jack Beven, these two systems possibly could qualify
as subtropical storms pending a careful analysis of all the
available data. For the time being they should be regarded as
possible subtropical storms.
(3) Subtropical portions of the tracks of Florence, Leslie, and Michael
are designated in the "best tracks" for these cyclones. The dates
of their subtropical phases, however, might not necessarily agree
with those David has assigned above.
(4) This storm has already been officially recognized as a subtropical
storm by TPC/NHC.
Part 1 (October summary), in addition to some introductory material,
contained David's discussions of two of the systems occurring in
October (Nrs VIII and XI in the table above). The November summary
(Part 2) featured some of the named tropical cyclones which exhibited
hybrid or subtropical characteristics for part of their lives. This
final installment discusses the remaining subtropical systems which
David identified: subtropical depressions in May and September (Nrs I
and IV) and a possible subtropical storm in August (Nr III).
I. Subtropical Depression, May 19-25. Satellite images and surface
analyses revealed a frontal wave developing south-southeast of Bermuda
on the 17th. Over the next couple of days, a 500-mb LOW cut off in
its vicinity, leading to occlusion. By the 19th the system became
devoid of fronts and had entered the subtropical stage. Its main
nontropical characteristic was a dry slot that encircled the center on
the 19th. Development of the cyclone occurred over 24 C waters and
convection was present well east and northeast of the center which
slowly warmed its core. The system reached its peak just as it entered
the subtropical stage, and weakened steadily thereafter as upper-level
winds out of the west began shearing the cyclone to the east, exposing
a low-level swirl on the 20th. The circulation became elongated on
the 23rd with multiple circulation centers before becoming absorbed
into a warm front on the 24th and 25th. No gale-force winds were
reported on the surface maps with this cyclone, though gales were
possible. The highest winds reported were 30 kts. (Some information
on this system was reported in the May global summary.)
III. Possible Subtropical Storm, August 28-30. Hurricane Debby had
dissipated in the northwestern Caribbean on the 24th. Some of its
weather spread northward as a cold front was invading northern Florida.
A tropical disturbance formed over 28 C waters in the inverted trough
ahead of the cold front on the 28th near the Bahamas as a closed 500-mb
LOW (with temps of -12 C at that level) was entering the scene from the
mid-Atlantic. The 29th featured a complex situation, as a mesoscale
convective complex formed to the east of the northward-moving LOW and
accelerated northeastward in an area (confirmed by ship reports) of
uniform southerly winds. The frontal boundary in the LOW's vicinity
had weakened, and thunderstorms were constricted to its east side as
winds aloft were westerly and its central pressure was falling.
On the 30th a tight circulation formed off North Carolina with a
small, concentrated area of thunderstorms as the LOW was swung around
the 500-mb LOW. Gale-force winds were reported by two buoys near the
coast, but existed only briefly as the system soon moved inland near
Wilmington and subsequently weakened. Operationally this LOW was
treated as a nontropical gale, but some local forecast discussions
addressed the cyclone as subtropical with one or two believing it to
be fully tropical. However, a large dry slot was present to the south-
west and south of the center--a definite nontropical characteristic.
As the LOW moved inland, it dumped an average of 50-75 mm of rain near
and to the right of its track from North Carolina west-southwestward
into northern Georgia. The closed low-level circulation dissipated
near Atlanta on the evening of the 30th.
More information on this system can be found in the global summary
for August. Jack Beven of TPC/NHC has indicated that all available
data for this cyclone will be carefully examined to see if it qualifies
for inclusion in the Best Track database as a subtropical storm.
IV. Subtropical Depression, September 10-11. A frontal wave formed
southwest of Bermuda on the 9th. The system quickly occluded and shed
its frontal boundaries by the 10th while sitting over 26 C waters. It
moved eastward as a cold front approached on the 11th, moving south of
the Azores. By the 12th the circulation had been absorbed into this
front. The highest winds seen were 20 kts via ship reports and land
observations, which were sparse.
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ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for December: No tropical cyclones
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NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for December: No tropical cyclones
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NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for December: 1 tropical depression **
1 typhoon ++
** - treated as a tropical depression by PAGASA only
++ - system did not reach typhoon intensity until early January, 2001
NOTE: Most of the information on each cyclone's history presented in
the narrative will be based upon JTWC's advisories, and references to
winds should be understood as a 1-min avg MSW unless otherwise noted.
However, in the accompanying tracking document I have made comparisons
of coordinates with JMA (Japan) and the Philippines (PAGASA) when their
positions differed from JTWC's by usually 40-50 nm or more. A special
thanks to Michael V. Padua, owner of the Typhoon 2000 website, for
sending me the PAGASA and JMA tracks.
In the title line for each storm I plan to reference all the cyclone
names/numbers I have available: JTWC's depression number, the
JMA-assigned name (if any), JMA's tropical storm numeric designator,
and PAGASA's name for systems forming in or passing through their area
of responsibility.
Northwest Pacific Tropical Activity for December
------------------------------------------------
As the month of December opened Tropical Storm Rumbia/Toyang was
in the process of crossing the southern Philippines. The storm moved
westward into the South China Sea, weakened into a tropical depression,
later re-intensified briefly into a minimal tropical storm, and finally
dissipated near the southern tip of Vietnam. (Please see the November
summary for the full report on Rumbia.)
A tropical disturbance developed early in the month east of the
Philippines and moved westward into the central portions of the
archipelago. JTWC never issued any warnings on this system, although
it was given a development potential of Fair on a couple of occasions.
PAGASA, however, upgraded the system to a tropical depression on
6 December and assigned the name Ulpiang. Tropical Depression Ulpiang
remained broad and disorganized but moved through the central
Philippines where it brought very heavy rains which led to extensive
flooding and loss of life. Based upon PAGASA's track (forwarded to me
by Michael V. Padua), Ulpiang's center crossed over the island of
Samar, then through the cluster of smaller islands lying to the west of
Samar, eventually reaching the vicinity of Mindoro where it weakened to
the point that warnings were discontinued.
According to Mike Padua, Naga City (his hometown) was flooded by
the rains of Ulpiang. Two stations south of Naga City (Lake Bato and
Ligao) each recorded 200 mm of rain in the 24-hour period ending at
6:00 am on the 8th. Ocampo, located a short distance southeast of the
city, recorded 160 mm in the same period. While Naga City itself
recorded only 68 mm, the city was flooded because it lies below sea
level and is in the catchment basin of the Bicol River (including its
tributaries). At least 20 fatalities were caused by the depression's
rains, the majority occurring on the island of Panay, although three
persons were killed in a landslide in the Bicol region of southeastern
Luzon. More than 50,000 persons were displaced when floods inundated
16 towns and Roxas City (on Panay). Many roads and bridges were
damaged and hundreds of hectares of rice fields and other farms were
flooded.
The final tropical storm of 2000 also became the first typhoon of
2001. Tropical Storm Soulik formed deep in the tropics east of the
southern Philippines late in the month, moved generally northward,
and as the month (and year) closed was headed northeastward out into
the Philippine Sea and weakening. However, on 3 January the storm
intensified with extreme rapidity into an intense 115-kt midget
typhoon which, after maintaining that intensity for only twelve hours,
encountered strong vertical shear and dry air and dissipated almost as
quickly as it had intensified.
Typhoon Soulik (TC-34W / TY 0023 / Welpring)
28 December - 5 January, 2001
---------------------------------------------
Soulik: contributed by the Federated States of Micronesia, is a
traditional Pohnpei Chief's title
The final NWP tropical cyclone of 2000 was at the same time the
first typhoon of 2001. After forming deep in the tropics east of
Mindanao and peaking at 55 kts on 31 December, Tropical Storm Soulik
had begun to weaken by 2 January and was forecast to continue to
dissipate. However, the capricious storm had other ideas. The
storm's intensity (based on JTWC's 1-min MSW estimates) literally
exploded on 3 January, increasing from 45 kts to 115 kts in just 18
hours! And then after only 12 hours, the storm weakened from a 115-kt
typhoon to a 25-kt dissipating depression in only 30 hours. Episodes
of such rapid intensification are rare in tropical cyclones, but none-
theless do occur and emphasize why even weaker storms which may appear
to be weakening should not be written off too soon. Rapid dissipation
of cyclones such as that exhibited by Soulik is also not common.
Soulik's demise was reminiscent of the decay of Typhoon Jack in
December, 1989. Jack weakened from 120 kts to 30 kts in a 30-hour
period.
An area of convection developed on 27 December about midway between
Palau and Mindanao. A broad LLCC was present with the most persistent
convection to the north. Vertical wind shear was weak and outflow was
fair. JTWC upgraded the development potential to Fair at 28/0600 UTC
and issued a Formation Alert at 28/1930 UTC. Organization had improved
with increased convective banding noted. A 28/1712 UTC TRMM pass
depicted a fully-exposed LLCC located about 200 nm east of the island
of Mindanao with the deep convection sheared to the north. The trend
toward further development continued and JTWC initiated warnings on
TD-34W at 29/0000 UTC. PAGASA also upgraded the disturbance to a
tropical depression at the same time and named it Welpring. A ship
report at 29/0000 UTC about 60 nm west of the center indicated a
northwesterly wind of 22 kts. The initial warning indicated that the
depression was quasi-stationary, but the next warning at 0600 UTC
relocated the center about 100 nm to the north of the previous warning
position based on visible satellite imagery and a 29/0143 UTC ERS-2
scatterometer pass. TD-34W/Welpring was moving slowly northward and
was forecast to continue this motion due to the steering influence of
a low- to mid-level ridge east of the system.
PAGASA was already estimating the 10-min avg MSW at 30 kts, but JTWC
increased their MSW estimate to 30 kts at 1200 UTC based on a synoptic
ship report of 28 kts. At 1800 UTC JTWC relocated the center of the
depression once more, this time to the west as the convection was
beginning to consolidate over the LLCC. TD-34/Welpring had also begun
to track to the northwest as it intensified. A synoptic ship report
of 35 kts around 30/0000 UTC led to the system's being upgraded to a
tropical storm by JTWC, PAGASA and JMA, with JMA assigning the name
Soulik. Soulik's center at the time was located approximately 200 nm
east of Surigao on the northern tip of Mindanao, moving northwestward
at 9 kts. This northwestward motion was forecast to come to a halt
and a northeasterly track commence as a mid-latitude trough approached
and weakened the ridge which was steering the storm. This forecast
soon came to pass. At 30/1200 UTC Tropical Storm Soulik reached the
westernmost point of its trajectory about 135 nm northeast of Surigao;
by 1800 UTC the storm was moving northeastward. Soulik's MSW had
reached 55 kts (per JTWC) by 0000 UTC on 31 December and the cyclone
maintained this intensity for three days before weakening some. (JMA's
estimated peak 10-min avg wind was 50 kts for the same 72-hour period.)
During this time Soulik moved generally on a northeastward to
east-northeastward course. Interestingly, at 1200 UTC on the 31st,
JTWC received satellite current intensity estimates of 45, 55, and
77 kts. The JTWC warning at 0000 UTC on 1 January noted that the
storm was located at the tail end of a long front extending southeast
across the Philippine Sea. The convection had become elongated,
although the LLCC still appeared to be organized. At 1800 UTC JTWC
relocated Soulik to a position 60 nm southeast of the previous warning
position or about 625 nm west-northwest of Guam. A 01/1534 UTC TRMM
pass depicted a partially-exposed LLCC southeast of the isolated deep
convection. A 700-mb HIGH east of the Mariana Islands with an
associated ridge extending southwestward over Mindanao was expected
to continue steering Soulik east-northeastward.
The storm continued to show signs of weakening on 2 January. Areal
extent of deep convection decreased and animated water vapor imagery
revealed transverse banding just north of the system, indicative of
strong westerlies aloft. JTWC and JMA both decreased their respective
MSW estimates to 45 kts at 02/0600 UTC. Satellite imagery around
1200 UTC showed that the LLCC was embedded about 60 nm under the cirrus
cloud shield, but a 02/0906 UTC SSM/I pass depicted weakening banding
and organization with a partially-exposed LLCC south of the deepest
convection. Soulik was forecast to continue weakening, but the storm
maintained its intensity throughout the day. The storm's forward
motion had slowed, thereby allowing deep convection to consolidate once
more around the center. JTWC increased the MSW to 55 kts at 0000 UTC
on the 3rd while JMA upped their maximum 10-min avg wind estimate to
50 kts. Soulik was at that time located about 570 nm south-southwest
of Iwo Jima and moving northward at 5 kts.
Shortly after 03/0000 UTC, however, the fireworks really started!
Based upon satellite intensity estimates ranging from 65 to 115 kts,
JTWC upgraded Soulik to a 105-kt typhoon at 0600 UTC. The storm had
intensified very rapidly during the previous six hours and sported a
7-nm round eye. A 200-mb analysis revealed an upper-level HIGH
developing over the system and animated water vapor imagery depicted
good outflow aloft. Typhoon Soulik reached its peak estimated
intensity of 115 kts (per JTWC) at 1200 UTC on 3 January when it was
located about 500 nm southwest of Iwo Jima. Satellite intensity
estimates were ranging from 90 to 127 kts. At its peak Soulik was a
small, symmetric system with intense central convection. 50-kt winds
extended outward from the center only 25 nm to the southeast and gales
covered an area only 140 nm in diameter. JMA's peak 10-min avg wind
estimate for Soulik was 80 kts at 03/1800 UTC. Even as the cyclone
reached its peak, cooler, drier air was impinging on its northwestern
quadrant and convection was beginning to elongate to the northeast.
As noted earlier, the demise of Typhoon Soulik was not much less
rapid than its intensification with the storm weakening (per JTWC's
MSW) from 115 kts to 25 kts in 30 hours. Strong vertical shear and
colder, drier air that was entrained into the system were the primary
culprits responsible for the quick extinction of Soulik. The MSW had
fallen to 65 kts--minimal typhoon intensity--by 1200 UTC on 4 January
when it was located about 440 nm southwest of Iwo Jima, and 12 hours
later Soulik was a dissipating depression. The 1200 UTC warning noted
that the weakening storm's motion had changed to the southeast, but the
final JTWC warning at 05/0000 UTC relocated the center about 170 nm to
the southwest of the previous analysis position (to a point about
700 nm east of Catanduanes Island in the Philippines). This relocation
was based upon the first visible satellite pictures of the day. The
intensity was lowered from 50 kts to 25 kts with animated satellite
imagery indicating a fully-exposed LLCC which was beginning to break
down on the southern side. (The JMV file for Typhoon Soulik, which
may be considered a first cut at a Best Track, begins to move the storm
back to the south-southwest at 04/1200 UTC and also reduces the MSW
to 55 kts at 1200 UTC and to 40 kts at 1800 UTC.) In its earlier
stages Tropical Storm Soulik/Welpring approached to within about 100 nm
of northern Mindanao in the Philippines and would likely have led to
some enhanced rainfall in the region, but the author has learned of no
damage or casualties resulting from this tropical cyclone. If any
come to light later they will be reported in a future summary.
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NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for December: 1 tropical cyclone of hurricane intensity
NOTE: The tracking and intensity information for North Indian Ocean
Basin tropical cyclones is based primarily upon operational warnings
from the Joint Typhoon Warning Center of the U. S. Air Force and Navy
(JTWC) at Pearl Harbor, Hawaii. Occasionally some information may
be gleaned from the daily Tropical Weather Outlooks and other bulletins
issued by the Indian Meteorological Department (IMD), which is the
WMO's RSMC for the basin.
The MSW are based on a 1-min averaging period, which is used by
all U. S. civilian and military weather services for tropical cyclone
warnings. For synoptic observations in the North Indian region,
both 10-min and 3-min average winds are employed, but IMD makes no
attempt to modify the Dvorak scale for estimating tropical cyclone
intensity; hence, a 1-min avg MSW is implied. In the North Indian
basin JTWC usually does not initiate warnings until a system is
well-organized and likely to attain tropical storm status within
48 hours.
North Indian Ocean Tropical Activity for December
-------------------------------------------------
As the month of December opened the remnants of Tropical Cyclone 03B
(which had reached hurricane intensity in November) were moving west-
ward across the Arabian Sea. The system briefly regained minimal
tropical storm intensity on the 3rd but had dissipated by the 6th
several hundred miles off the coast of Somalia. The final NIO tropical
cyclone of the year formed on Christmas Day east of Sri Lanka and
struck the island as a hurricane on the 26th. The system then began
to weaken, moved over the southern tip of India, and had dissipated
by the 29th.
Tropical Cyclone (TC-04B)
25 - 28 December
--------------------------
Almost exactly a month after the last Bay of Bengal storm formed,
another tropical cyclone formed in the Bay and also reached minimal
hurricane intensity. TC-03B in November had struck southeastern India
near Pondicherry, but this month's TC-04B followed a very low-latitude
track and became the first tropical cyclone to strike the island nation
of Sri Lanka since TC-10B struck the island with 55-kt winds on
12 November 1992. That particular storm left 13 persons dead in Sri
Lanka, and later claimed over 200 lives in extreme southern India
where it struck with 70-kt winds on the 13th. (This information was
gleaned from some of Jack Beven's Weekly Global Tropical Cyclone
Summaries, which were the predecessors to the current series of monthly
summaries.) TC-04B was the first tropical cyclone of hurricane
intensity in the Bay of Bengal in the month of December since TC-08B
in 1996. (In 1998 TC-08A reached minimal hurricane intensity in the
Arabian Sea in mid-December.)
Because of its very low latitude (the northern tip is just south of
10N), and also by virtue of its being located in a basin with a low
frequency of tropical cyclone formation, Sri Lanka only rarely receives
a direct strike by one of these storms. At present the author does not
know the last occasion prior to 2000 when a tropical cyclone of full
hurricane intensity struck the island. No hurricanes have struck Sri
Lanka since at least 1987. In November, 1978, a hurricane (designated
as TC 21-78 by JTWC) struck the island with 95-kt winds near Batticaloa
where sustained winds of 85 kts were reported two hours before the
center reached the coast. More than 1000 lives were lost in that
cyclone and many thousands of acres of crops were destroyed by the
storm's winds, rain, and associated storm surge. (This information
was taken from the 1978 Annual Typhoon Report from JTWC.)
A STWO issued by JTWC at 1800 UTC on 21 December mentioned that an
area of convection had developed and persisted very deep in the tropics
in the central Bay of Bengal. The convection was in a region of weak
vertical wind shear and a QuikScat pass indicated a possible LLCC. The
disturbance remained quasi-stationary over the next couple of days, and
by the 23rd central convection had increased and a mid-level cyclonic
circulation had begun to develop. The system had moved westward and
was located about 240 nm east of Sri Lanka at 23/0700 UTC when the
first of two Formation Alerts was issued. The disturbance continued
to slowly become better organized and a second Formation Alert was
issued at 24/0700 UTC when the LLCC was located approximately 140 nm
east of Sri Lanka. A 23/2338 UTC QuikScat pass indicated that the weak
LLCC was located south of the main convection and JTWC estimated the
maximum winds at 20-25 kts.
The STWO issued at 24/1800 UTC noted that animated satellite imagery
depicted a decrease in overall organization with some weakening of the
convection; however, this trend apparently soon reversed itself: at
0600 UTC on the 25th JTWC issued the first warning on TC-04B with an
initial warning intensity of 40 kts. The cyclone was located about
135 nm east of Sri Lanka and was drifting westward at 2 kts. Satellite
imagery indicated that the LLCC had moved under the deep convection,
thus leading to the increase in Dvorak numbers. A subtropical
ridge to the north steered the storm slowly westward as it steadily
intensified. The MSW had reached 55 kts by 1800 UTC and animated
infrared imagery showed improving organization with good outflow in
all quadrants. A 25/1602 UTC SSM/I pass depicted the primary
convective band wrapping tightly into the system center.
The center of TC-04B made landfall around 0600 UTC on 26 December
in eastern Sri Lanka near Trincomalee with the MSW estimated at 65 kts.
Although the cyclone weakened some while over land, it maintained its
organization rather well. By 0600 UTC on the 27th the storm's center
had emerged back over water along the western coast of Sri Lanka with
the MSW estimated at 50 kts. The cyclone was forecast to slowly
re-intensify for at least the next 48 hours, but this failed to happen.
The intensity was decreased to 45 kts at 1800 UTC as satellite imagery
had indicated weakening convection and decreasing organization during
the previous few hours. The center of TC-04B was located about 120 nm
northwest of Colombo, Sri Lanka, but most of the deep convection lay
to the west-northwest of the center over southern India.
By 0600 UTC on 28 December the system had reached the coast of
extreme southern India and was centered about 25 nm northeast of Cape
Comorin. Convection had continued to weaken and become less organized,
and most of the deeper convection was sheared to the west-northwest of
the LLCC. JTWC decreased the MSW to 35 kts at 0600 UTC, and issued
the final warning on the system at 1800 UTC with the rapidly weakening
center still over land about 40 nm north-northwest of Cape Comorin.
What little convection remained was very weak and displaced well north
of the system's center; satellite imagery showed primarily low- and
mid-level clouds near the center.
Even though only a minimal hurricane at landfall, the cyclone was
quite destructive to Sri Lanka. Fortunately the death toll was low:
seven fatalities was the highest reported number available to the
author. However, over 75,000 families were left homeless (upwards of
half a million individuals) in the districts of Ampara, Batticaloa,
Mannar, Anuradhapura, Trinacomalee, and Polonnaruwa. The fishing
village of Pulmudai was reportedly destroyed, and about 20,000 hectares
of rice fields were damaged. Many of the affected areas had already
been experiencing flooding due to monsoon rains and the cyclone served
to exacerbate the flooding. (In the Ampara district 94,000 persons had
been rendered homeless in late November due to flooding from monsoon
rains.) There was some wind-related damage reported: several police
stations and military camps had their roofs blown off due to strong
winds gusting between 80 and 95 kts (more than likely estimated
values). Also, apparently many homes experienced the loss of their
roofs--a report indicated that tens of thousands of people were being
housed in temporary shelters due to the winds sweeping away the roofs
of their houses. In southern India, heavy rains reportedly fell in
the Tuticorin region of Tamil Nadu state but no damage or casualties
were mentioned in the press report.
***********************************************************************
SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E
Activity for December: No tropical cyclones
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NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E
Activity for December: 1 severe tropical cyclone
NOTE: The primary sources of information for Australian Region
tropical cyclones are the warnings and bulletins issued by the three
TCWC's at Perth, Darwin, and Brisbane. Information gleaned from
JTWC's warnings was used as a supplement for times when it was
impossible to obtain Australian bulletins and for comparison purposes.
References to sustained winds should be understood as being based on a
10-min averaging period unless otherwise noted.
A description of the Australian Cyclone Severity Scale, which is
alluded to in the narrative below, can be found in Chris Landsea's FAQ
on HRD's website:
http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqD.html#D2>
or on Michael Bath's Australian Severe Weather site:
http://australiansevereweather.com/cyclones/history.htm>
A special thanks is due to Mark Kersemakers of the Darwin TCWC for
forwarding to me a summary of Tropical Cyclone Sam. Also, a special
thanks to Carl Smith, a cyclone enthusiast who lives on Queensland's
Gold Coast, for sending me a report he'd written on Sam from which I
extracted some information. Much tropical cyclone-related information
can be found on Carl's website:
http://www.ace-net.com.au/~carls/>
Northwest Australia/Southeast Indian Ocean
Tropical Activity for December
------------------------------------------
The 2000-2001 tropical cyclone season in northwestern Australia got
off to a start in a manner remarkably similar to the previous year.
In early December, 1999, a very intense Cyclone John made landfall at
Whim Creek, just east of Roebourne, as a Category 5 cyclone on the
Australian Cyclone Severity Scale. This year's Cyclone Sam made land-
fall also as a Category 5 cyclone (perhaps only slightly less intense
than John) in Western Australia, but about 400 km to the east near
Bidyadanga, southwest of Broome. (In 1999 a much weaker Tropical
Cyclone Ilsa followed on the heels of John and made landfall a few days
later in the same general area as this year's Tropical Cyclone Sam.)
Actually, this was the third consecutive year to feature a December
Category 5 cyclone making landfall in northwestern Australia. In
December, 1998, Severe Tropical Cyclone Thelma battered Darwin with
hurricane-force gusts and eventually made landfall at peak intensity
along the Kimberley coast near the Northern Territory/Western Australia
border. However, the 1998-1999 season had gotten off to a very early
start with Cyclone Zelia forming farther out in the Southeast Indian
Ocean in early October, followed by Alison in November and Billy in
early December.
Severe Tropical Cyclone Sam (TC-03S)
3 - 10 December
-------------------------------------
The daily TWO from Darwin on 28 November mentioned that a broad
area of low pressure had formed in the southeastern Arafura Sea west
of the Cape York Peninsula. The LOW moved steadily westward for the
next few days, passing north of the Northern Territory's Top End on
the 29th and 30th, and by 1 December had reached a point in the Timor
Sea about 230 nm northwest of Darwin and became quasi-stationary. A
STWO issued by JTWC at 0300 UTC on 1 December indicated persistent
convection in the area with fair outflow aloft. The Darwin TCWC began
issuing tropical cyclone advices on the LOW at 5:00 pm CST on the
2nd (0730 UTC). The center of the still-broad circulation was located
about 250 nm northwest of Darwin and was moving slowly southwestward.
The STWO issued by JTWC at 1800 UTC on the 2nd indicated that outflow
had improved and convection was becoming increasingly organized.
Darwin began issuing High Seas gale warnings at 03/0600 UTC as the
LOW continued to show signs of further development. The system moved
generally very slowly southward over the next 24 hours and had reached
the Kimberley coast by 0130 UTC on the 4th about 90 km (50 nm) east of
Kalumburu. The center of the LOW tracked farther inland as it
moved west-southwestward over the north Kimberley region. This track
over land delayed the strengthening of the system, but once it moved
back out over the warm Timor Sea waters, intensification proceeded at
a steady pace. At 04/1800 UTC the center of the LOW was relocated
north of the previous position to a point on the coastline about
180 km (100 nm) west-southwest of Kulumburu and 480 km (260 nm)
northeast of Broome. The center was moving westward at 8 kts out
into the Timor Sea.
JTWC issued a Formation Alert at 04/1700 UTC, noting that the system
was beneath the subtropical ridge and the development potential was
considered good. The Perth TCWC assumed warning responsibility for the
developing tropical cyclone at 04/2200 UTC as the center had moved west
of 125E, and JTWC issued their first warning on TC-03S at 05/0000 UTC.
The LOW was christened Tropical Cyclone Sam at 0400 UTC when it was
centered about 75 nm north of Kuri Bay. The 10-min avg MSW was
estimated to be around 40-45 kts. A 05/0958 SSM/I pass depicted a
partially-exposed LLCC with convection displaced to the southwest. At
the time Sam was north of the subtropical ridge axis under 15 to 25-kt
northeasterly flow which was inhibiting development somewhat. The
cyclone's intensity increased slowly for about 48 hours after being
upgraded as it moved westward off the coast of Western Australia.
Perth had increased the MSW to 55 kts by 2200 UTC on the 5th while
JTWC's 1-min avg MSW was lower at 45 kts. However, JTWC estimated
that the peak 1-min avg MSW had reached 55 kts by 06/1200 UTC. Sam's
convective organization was improving and the storm was under favorable
outflow aloft. A 06/0945 UTC SSM/I pass depicted a primary band of
convection on the west wrapping into the northern quadrant of the
system. At 1000 UTC on 6 December the cyclone's center was located
approximately 170 nm north-northwest of Broome and moving toward the
west-southwest at 5 kts.
Sam's motion became increasingly southwestward during the evening
(local) of the 6th. JTWC increased the 1-min avg MSW to 65 kts in the
07/0000 UTC warning based on satellite intensity estimates. Animated
satellite imagery depicted increasing organization with a tightly-
curved banding eye feature, a feature which had been noted earlier in
microwave imagery. Perth's 10-min avg MSW was in good agreement: at
2200 UTC the estimate was 60 kts and the intensity was increased to
70 kts at 0400 UTC on the 7th, making Sam a Category 3 cyclone. The
storm's center was then located about 65 nm northwest of Broome, or
approximately 90 nm north-northwest of Bidyadanga, moving south-
southwestward at 6 kts. During the late afternoon and evening (local)
of 7 December Tropical Cyclone Sam began to intensify rapidly into
a very severe cyclone. Perth upgraded the storm to a Category 4
cyclone at 1400 UTC (10:00 pm WST) and JTWC issued an offtime warning
at 1800 UTC (JTWC normally issues warnings every 12 hours for Southern
Hemisphere cyclones) to upgrade the MSW to 115 kts (up from 85 kts six
hours earlier). Sam was sporting a well-defined 25-nm diameter eye at
this time, although the storm was under some moderate vertical wind
shear. (According to Mark Lander, around 07/1200 UTC the objective
(digital) Dvorak rating for Sam reached T7.7!)
The cyclone, after moving to the south-southwest, slowly jogged for
awhile a bit more to the southwest before turning southeastward toward
the coast. By 2000 UTC Perth had upgraded Sam to a Category 5 cyclone
with an estimated CP of 920 nm and peak gusts estimated at 150 kts--
corresponding to a maximum 10-min avg wind of about 105 kts. Sam
became almost stationary for a few hours about 65 nm northwest of
Bidyadanga before commencing the southeastward movement that would
carry it inland near the same community. At 0600 UTC on 8 December
JTWC increased the 1-min avg MSW estimate to the peak value for the
storm of 125 kts. The eye, well-defined and about 15 nm in diameter,
was centered about 40 nm west-northwest of Bidyadanga, moving south-
eastward at about 7 kts. The center of Severe Tropical Cyclone Sam
crossed the coast just west of Bidyadanga around 1100 UTC (7:00 pm WST)
on 8 December at its peak intensity. By 1600 UTC the eye had just
about completed crossing the coast with the center inland to the south
of Bidyadanga. Convection was beginning to weaken but radar imagery
revealed a strong convective band northwest of the eye moving onshore
near La Grange Bay.
After making landfall the powerful cyclone continued moving south-
eastward across the Great Sandy Desert as it slowly weakened. By
08/2200 UTC the center of the by-now Category 3 cyclone was located
approximately 100 km south-southeast of Bidyadanga with peak gusts
estimated at 110 kts. The final warning from JTWC was issued at
0600 UTC on 9 December with the MSW (1-min avg) still estimated
at 65 kts. The warning noted that although convection was weakening,
Sam still maintained some tightly-wrapped banding features. At
09/1000 UTC Sam's center was located 165 km northeast of Telfer and
moving southeastward at 15 km/hr. Gusts exceeding hurricane force were
still reported to be occurring near the center. The storm was down-
graded to a Category 1 cyclone at 1300 UTC, and the final advice was
issued on the weakening Sam at 1200 UTC on the 10th (8:00 pm WST),
placing the center about 305 km east of Telfer. The advice indicated
that there was still a possibility of a few gales with gusts reaching
near 50 kts, but those were expected to moderate within a few hours.
The remnants of Tropical Cyclone Sam persisted as a rain-bearing LOW
for several days as it drifted eastward across northern Australia.
Most of the 200-plus residents of the Aboriginal community of
Bidyadanga were evacuated before the cyclone struck; however, press
reports indicated that around 30 persons elected to remain behind and
ride out the storm (although a later report mentioned that only three
people refused to leave). Major structural damage appeared to be
light with only a few buildings severely damaged, but many trees, power
lines, sheds and fences were downed. The Anna Plains homestead station
south of Broome was extensively damaged with staff quarters and sheds
demolished. The station also lost power and water during the cyclone.
Shelamar reported 520 mm of rainfall in the 48 hours ending at 9:00 am
on 11 December, but most of this likely fell within a 24-hour period
since the community was evacuated for a time and no 24-hour reading
was taken.
There was a report from Reuters that 163 illegal immigrants were
feared drowned after two boats which had left Indonesia, bound for the
Ashmore Islands (about 600 km off the coast of northwestern Australia),
had been caught in Tropical Cyclone Sam and sank. A Japanese tanker
reportedly picked up four survivors. This story has apparently never
been confirmed, but there is no reason to doubt it since five boatloads
of illegal immigrants did arrive in Australian waters in the week
following the cyclone, proving that refugee-laden boats were in the
area at the time.
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NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E
Activity for December: 1 tropical LOW
NOTE: The primary sources of information for Australian Region
tropical cyclones are the warnings and bulletins issued by the three
TCWC's at Perth, Darwin, and Brisbane. Information gleaned from
JTWC's warnings was used as a supplement for times when it was
impossible to obtain Australian bulletins and for comparison purposes.
References to sustained winds should be understood as being based on a
10-min averaging period unless otherwise noted.
Northeast Australia/Coral Sea
Tropical Activity for December
------------------------------
No tropical cyclones formed in the Gulf of Carpentaria or Coral Sea
during December; however, a tropical LOW formed on the 4th very near
the tip of the Cape York peninsula and moved southwestward across
the Gulf, making landfall around 0130 UTC on the 6th about 90 nm south-
west of Alyangula or about 75 nm west-northwest of Port McArthur.
The Brisbane TCWC issued three advices on the LOW before passing
warning responsibility to Darwin. It was initially felt that the LOW
might develop into a tropical cyclone, but by the time Darwin had
assumed responsibility for issuing advices, the system had not gotten
any better organized and was rapidly approaching the coastline in the
southwestern Gulf of Carpentaria region. One factor which probably
worked against this LOW's developing into a cyclone was its somewhat
rapid rate of movement: for most of its life it moved southwestward
across the Gulf at speeds of around 16 to 19 kts--rather fast for that
part of the world--which likely made it more difficult for the system
to consolidate its convection, and if nothing else, significantly
decreased the time spent over the warm waters of the Gulf before making
landfall.
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SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E
Activity for December: 2 tropical depressions
NOTE: Most of the information presented below was taken from the
operational warnings and advisories issued by the Fiji TCWC at Nadi.
References to sustained winds imply a 10-minute averaging period
unless otherwise noted.
South Pacific Tropical Activity for December
--------------------------------------------
There were no tropical cyclones in the South Pacific basin during
December, but the Nadi TCWC did issue gale warnings on two tropical
depressions during the month. TD-01F formed about 200 nm west of
Fiji on 11 December and moved eastward toward the islands. Apparently
no gales actually occurred during this phase of the system's life and
advisories were discontinued at 12/2100 UTC as the system was moving
southeastward into an area of increased shear and cooler SSTs. Gale
warnings, however, were re-initiated at 14/0000 UTC. The depression
by this time had moved rapidly eastward and was located about 300 nm
east-southeast of the Kingdom of Tonga. Some gales were occurring over
an extensive area along the southern periphery of the system, but it
seems likely that the depression was not fully tropical during its
latter warning phase. The system remained quasi-stationary in the area
until the final gale warning was issued at 15/1200 UTC.
A report from the Office for the Coordination of Humanitarian
Affairs stated that a tropical depression (which undoubtedly must have
been TD-01F) crossed Fiji and brought gusty winds, thunderstorms and
bands of continuous rainfall. Rivers reportedly burst their banks,
flooding low-lying areas. Two persons drowned and two others were
reported missing at sea. Roads and bridges were submerged in some
areas and power outages were reported. Minor landslides occurred and
damage was reported to root crops and other vegetables.
Another tropical depression (likely more of a hybrid) formed far to
the southeast of Tahiti (about 375 nm west-northwest of Pitcairn) on
18 December. This system was accompanied by some peripheral gales well
north and east of the center. The system moved fairly quickly eastward
and the final warning, issued at 19/1200 UTC, placed the center about
275 nm east of Pitcairn Island.
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EXTRA FEATURE
In order to shorten the amount of typing in preparing the narrative
material, I have been in the habit of freely using abbreviations and
acronyms. I have tried to define most of these with the first usage
in a given summary, but I may have missed one now and then. Most of
these are probably understood by a majority of readers but perhaps a
few aren't clear to some. To remedy this I developed a Glossary of
Abbreviations and Acronyms which I first included in the July, 1998
summary. I don't normally include the Glossary in most months in
order to help keep them from being too long. If anyone would like to
receive a copy of the Glossary, please e-mail me and I'll be happy
to send them a copy.
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AUTHOR'S NOTE: This summary should be considered a very preliminary
overview of the tropical cyclones that occur in each month. The cyclone
tracks (provided separately) will generally be based upon operational
warnings issued by the various tropical cyclone warning centers. The
information contained therein may differ somewhat from the tracking and
intensity information obtained from a "best-track" file which is based
on a detailed post-seasonal analysis of all available data. Information
on where to find official "best-track" files from the various warning
centers will be passed along from time to time.
The track files are not being sent via e-mail. They can be retrieved
in the following manner:
(a) FTP to: hrd-type42.nhc.noaa.gov [140.90.176.206]
(b) Login as: anonymous
(c) For a password use your e-mail address
(d) Go to "data" subdirectory (Type: cd data)
(e) Set file type to ASCII (Type: ascii)
(f) Transfer file (Type: get remote_file_name local_file_name )
(The files will be named with an obvious nomenclature--using
December as an example: dec00.tracks)
(g) To exit FTP, type: quit
Both the summaries and the track files are standard text files
created in DOS editor. Download to disk and use a viewer such as
Notepad or DOS editor to view the files.
The first summary in this series covered the month of October,
1997. If anyone wishes to retrieve any of the previous summaries,
they may be downloaded from the aforementioned FTP site at HRD. The
summary files are catalogued with the nomenclature: dec00.sum, for
example.
Back issues can also be obtained from the following websites
(courtesy of Michael Bath, Michael V. Padua, Tom Berg, Michael
Pitt, and Rich Henning):
http://australiasevereweather.com/cyclones/>
http://www.typhoon2000.com> OR http://www.geocities.com/taifun00/>
http://www.hurricanealley.net/>
http://www.qisfl.net/home/hurricanemike>
http://www.met.fsu.edu/gsc/Docs/Grads/henning/cyclones/>
Another website where much information about tropical cyclones may
be found is the website for the UK Meteorological Office. Their site
contains a lot of statistical information about tropical cyclones
globally on a monthly basis. The URL is:
http://www.met-office.gov.uk/sec2/sec2cyclone/sec2cyclone.html>
TROPICAL CYCLONE REPORTS AVAILABLE
I have discovered that JTWC now has available on its website the
complete Annual Tropical Cyclone Report (ATCR) for 1999 (1998-1999
season for the Southern Hemisphere). Also, ATCRs for earlier years
are available also.
The URL is: http://199.10.200.33/jtwc.html>
Also, TPC/NHC has available on its webpage nice "technicolor"
tracking charts for the 2000 Atlantic and Eastern North Pacific
tropical cyclones; also, preliminary storm reports for all the 2000
Atlantic and Eastern North Pacific cyclones are now available.
The URL is: http://www.nhc.noaa.gov>
Prepared by: Gary Padgett
E-mail: [email protected]
Phone: 334-222-5327 (nights & weekends) / 850-882-2594 (weekdays)
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